Fish species associations in riffle habitat of streams of varying size and acidity in New Brunswick and Nova Scotia

Factors related to stream size and alkalinity were most influential in determining fish species associations in three catchments of New Brunswick (NB) and Nova Scotia (NS) Canada, as determined by discriminant function analysis of TWINSPAN stream site classification. In the circumneutral Saint Croix (NB) catchment, the creek chub, Semotilus atromaculatus (Mitchill), brook trout, Salvelinus fontinalis (Mitchill), blacknose dace, Rhinichthys atratulus (Hermann), Atlantic salmon, Salmo salar Linnaeus, eel, Anguilla rostrata (Lesueur) and fallfish. Semotilus corporalis (Mitchill) dominated stream sites of progressively greater discharge and higher median mid‐summer temperature. In the acidic Gold (NS) system, the brook trout, Atlantic salmon, and eel exhibited a distribution pattern in relation to stream size and temperature similar to that for the Saint Croix, with the eel relatively more abundant in the Gold at large stream sites. The creek chub was excluded from the smallest tributaries by low pH. The ranges of blacknose dace and fallfish do not extend to southwestern Nova Scotia. In the Medway (NS) system (slightly more acidic than the Gold), the relative abundance of Atlantic salmon is reduced, and that of eel increased as compared with the Gold and Saint Croix systems. The lower limiting mid‐summer pH levels for creek chub, salmon, brook trout, and eel are 5.2, 5.0, 4.7 and